The crystal oscillator is typically the source of frequency stability for various communications systems. The crystal is typically made of quartz and has resonating capabilities. Quartz is a material with piezoelectric properties that can be cut at certain angles and thicknesses to provide electrical and mechanical stability in radio frequency (RF) circuit designs. A typical crystal oscillator can be manufactured to achieve tolerances of less than 10 ppm (parts per million), but larger tolerances tend to be less expensive to manufacture. The crystal can be “tuned,” that is, adjusting the resonant frequency to a desired frequency through open-loop or closed-loop control in order to achieve tighter tolerances or to ease manufacturing requirements.
Because the crystal oscillator is an inherently stable resonator, this oscillator can be used in many types of electronic oscillator circuit topologies. For example, these oscillator circuit topologies can include the Colpitts, Hartley, and Pierce oscillator circuit topologies.